The present invention relates to data processing in computer systems, and in particular, to reducing flicker when displaying HTML images on a television monitor.
Networking technology has developed a large network of networks, referred to as the Internet, which interconnects millions of computers around the world. The Internet allows the transfer of data between any number of computer systems connected to the Internet using the Transmission Control Protocol/Internet Protocol (TCP/IP). Computers responding to service requests from other computers, via the Internet, are commonly referred to as servers, and computers that initiate requests for service from a server are referred to as clients.
The Internet has become very popular in part due to the World Wide Web (WWW), which is a network of links to hypertext documents operating within the Internet. These hypertext documents are referred to as either Web documents, Web pages, or hypertext documents. Web documents are embedded with directly accessible connections or links to other documents which create a non-linear way of reading the document. The links are embedded in Web documents as a phrase of text or an image which can be selected and activated by a computer user. Information about the Web documents are controlled and provided by Web servers. At the user""s end, a Web client takes the user""s requests and passes them on to the Web server.
The Web documents are written with a high level programming language referred to as the Hypertext Markup Language (HTML). Commands of the HTML, hereinafter referred to as tags, provide a variety of functions including, but not limited to, defining special format and layout information in a Web document, embedding images and sound in a Web document, and embedding links to other Web documents.
This platform independence is one of the significant advantages of the WWW, since a web page creator need only create a single definition of a web page in HTML. Thus, no matter what sort of computer is used by a user browsing the WWW, the web page can be viewed with high quality.
The navigation model offered by the WWW is so powerful and ubiquitous that it provides a revolutionary new way to publish and access information throughout the world. One drawback of the WWW, however, is that current use is limited to computer operators. This is an enormous impediment to the WWW""s reach and potential to impact human civilization. Although many people have access to computers at work, home and school, the vast majority of people in the world do not have access to computers, particularly outside the United States. Furthermore, of the computers that are in use throughout the world, a relatively small percentage are capable of browsing the WWW. Moreover, the requirement of owning a computer to access the WWW continues to be the largest force inhibiting the world from accessing the WWW because of computers"" high cost, required space and complexity of operation. A solution to these drawbacks would be to develop a dedicated WWW browsing computer that utilizes a television for displaying information. Since this device would be dedicated to the function of the WWW, and would not include a disc or monitor, there could be significant cost and space savings. Moreover, it could simplify use and access of the WWW. Most importantly, since almost all homes in industrialized countries already have a television, access to the WWW using existing televisions could reach a virtually unlimited number of people. Simplicity could provide the novice with easy access to the information provided by the WWW.
In order to access, process, and display a Web document, a client uses a first set of instructions, referred to as a browser. The browser typically includes a set of browser commands corresponding to the tags available in the HTML. Each browser command in turn points to a procedure of one or more instructions defining the command which, when executed, provide a functionality of the respective command. If the client requires service from the Web server, the browser uses the Hypertext Transfer Protocol (HTTP) to communicate with the server.
The browser compares each tag found embedded in a Web document with the set of browser commands. Once a match is found, the browser executes the procedure corresponding to the matched browser command in order to provide the functionality of the respective command.
The instructions of the browsers are typically written with a programming language different from the HTML, which includes a library of several routines. The library of routines can in turn be used to develop and add new browser commands, or modify existing browser commands, which can be embedded in a Web document as new or modified tags to provide new functionality when displaying the Web document.
Various manufacturers have announced and begun producing television based WWW browsing computers including Bandai Pippin(trademark), the Oracle NC (CR Oracle Corp.), the Viewcall Webster (CR Viewcall) and the Sega Saturn (CR Sega Corp.). However, because of the fact that WWW was originally designed for high resolution computer monitors and not for televisions, these devices provide marginal or unsatisfactory display quality for the WWW browser. One of the biggest problems is interlace image flickering. For example, interlace image flicker is a serious problem if the WWW page displayed happens to have coherent high frequencies in the vertical dimension, for example, 1-pixel wide horizontal lines, because of the interlacing techniques used by NTSC, PAL and SECAM TV systems.
Various devices, such as Bandai Pippin, generate a flicker free interlace image; however, in doing so, they blur images on the television screen unnecessarily. While some images on the WWW have coherent high frequencies that result in interlace flicker, most images do not have this problem. Conventional devices, such as the Bandai Pippin displays subsystem, uses a 1-2-1 vertical convolution to all images, resulting in blurred images due to the application of a filter technique to all images regardless of whether or not the images flicker. Furthermore, given that televisions already provide a low resolution image relative to computer monitors, unnecessary blurring takes a marginal display device and reduces its image quality even further.
One example of a device providing filtering for an interlace image is U.S. patent application No. 5,005,011 of Perlman, et al. (xe2x80x9c""011 patentxe2x80x9d). The filtering method disclosed in the ""011 patent is one example of a filtering method commonly used in WWW browsing devices and will be referred to here for illustration. Furthermore, the ""011 patent is hereby incorporated by reference as background material for the device described and claimed herein.
As taught in the ""011 patent, images with coherent high frequencies in the vertical dimension that are displayed on an interlaced display are perceived by a human observer to be flickering. Flickering images are almost universally perceived by human observers as unpleasant to watch. Furthermore, prolonged viewing can result in headaches, nausea or motion sickness. Thus, viewing a web page suffering from interlace flicker for a prolonged period is undesirable.
Generally, web pages are designed for display on progressive scan computer RGB monitors. Progressive scan displays have an advantage over interlace displays, for example televisions, in that, regardless of the spatial frequency profile of a displayed image, progressive scan displays do not suffer from visually disturbing line flicker problems. Consequently, in current web page design practice, images are selected without regard to their spatial frequency profile and, as may be expected, a web page displayed without flicker reduction filtering on an interlace display will often suffer from unsightly line flicker problems.
Some images on the WWW contain the high coherent spatial frequencies in the vertical dimension that cause interlace flicker, where some do not. For example, images of natural scenes, which typically do not have coherent high frequencies, do not have flicker problems. On the other hand, images that are generated synthetically with computer drawn thin lines that have coherent high frequencies can be subject to flicker. In another example, images that are captured from video cameras which, by their nature, due to a well known video engineering in the parameter called the Kell factor, are limited in bandwidth in the spatial frequency domain so that they do not flicker.
Some images are represented by character codes rather than a specifically defined two dimensional array of pixels such as, for example, text fields. The two dimension pixel realization of such images is designed by the browser, resulting in a situation in which the same character codes may result in a different image realization from one browser to another. This can be further varied from one user to another using the same browser if the users select different fonts. For example, depending on the spatial frequency characteristics of the fonts chosen by the browser, the image generated by a text field may or may not result in interlace flicker.
One option that may be considered is pre-filtering an image before it is posted on a web with some type of flicker reduction method. Although this is a possible means to reduce interlace flicker, it has the undesirable side effect of unnecessarily blurring the posted Web page images when they are displayed on progressive scan monitors which do not suffer from line flicker. Since one of the most powerful aspects of the Web is the ability of a Web page designer to post a single Web page that can be displayed with high quality on any platform, pre-filtering an image so as to compromise its quality on a progressive scan platform is undesirable.
Therefore, a great need exists for a device that can display a video image from the WWW on a television screen with a reduction of flicker effects without unnecessarily blurring the image. As will be seen, the present invention accomplishes this in a simple and elegant manner.
A method and apparatus are provided for reducing flicker of a display image defined in HTML format for display on a television monitor. One embodiment of the present invention incorporates a tag that may be attached to an image to be displayed on a television monitor. This is done by a particular tag that designates a file name which includes object or image data stored in a file. The tag identifies an image as either having a frequency profile that will result in interlace flicker or as having a frequency profile that will not result in interlace flicker. When a World Wide Web (WWW) browser employing this embodiment encounters such a tag, it will apply flicker reduction filtering to the image when the tag identifies the image as having a frequency profile that results in interlace flicker. Otherwise, the browser displays the image without filtering.